Medusa, Caravaggio (c 1598)

Artist:Michelangelo Merisi da Caravaggio (1571-1610) was known in late 16th-century Rome for the naturalism and lifelike freshness of his painting. The compelling reality of Caravaggio's painting, however, does not make him a "realist". On the contrary, his art is fantastic and his representation of the natural world uses mimesis to intensify erotic and religious vision.

We are so confused by the warm flesh of the angel in The Rest on the Flight into Egypt that we accept the strangest thing about him: he has wings; we are so fixated on the brightness of Caravaggio's compositions that the abstract mystery of their setting only registers unconsciously, as a given of the inexplicable.

Later, Caravaggio was to change his manner, becoming more elusive, his space smokier, his figures less seductive. In his naturalistic mode, Caravaggio makes the impossible real and the real a lurid dream.

Subject: This severed head is that of Medusa, the gorgon who had hair of living snakes. Such was her repulsiveness that anyone who looked at her was turned to stone. The hero Perseus used a shining shield from the goddess Athena to avoid looking at Medusa directly, then decapitated her.

Distinguishing features: She - or he, as Caravaggio's model is a male youth - is portrayed in the very moment of self-recognition. This is both a horrific and horrified image, as the eyes of the gorgon are fixed forever on the terrible realisation of who he or she is. This recognition is so devastating that it has destroyed Medusa's connection with reality, with the body, with any external context. There is nothing here but a head, severed but still conscious, an image of one of the great nightmares, that of the decapitated head aware of its disembodied condition.

Blood pours from it in thick streaks. The mouth is a cave with teeth bared, leading into the terrible prison of the head. Most odiously real of all is the mane of writhing serpents: not vague fancies but accurately observed.

Caravaggio was commissioned to make this monstrosity as a gift for the Grand Duke of Tuscany; conceived to enter the Medici collection in Florence, it would enable Caravaggio to compete with Leonardo da Vinci, by this time dead for 80 years. This painting decorates a convex wooden shield, surely alluding to a story about the young Leonardo, whose father once asked him to decorate a shield. Leonardo went into the fields, collected snakes, lizards and insects, and assembled them into a hybrid monster which he painted on the shield.

The tale of Leonardo's monster is about art and power: decorating a warlike object, the artist imposes his imagination on the world, creates an image with disturbing power. That is what Caravaggio does here.

Inspirations and influences: Decapitation is a recurrent image in Caravaggio's painting: Judith Beheading Holofernes, The Beheading of St John the Baptist, and Salome Receives the Head of St John the Baptist.